Filtering an embedded array in MongoDB

Question

I have a Mongodb document that contains an an array that is deeply imbedded inside the document. In one of my action, I would like to return the entire document but filter out the elements of that array that don't match that criteria.

Here is some simplified data:

{
   id: 123 ,
   vehicles : [
     {name: 'Mercedes', listed: true},
     {name: 'Nissan', listed: false},
     ...
   ]
}

So, in this example I want the entire document but I want the vehicles array to only have objects that have the listed property set to true.

Solutions

Ideally, I'm looking for a solution using mongo's queries (e.g. `$unwind, $elemMatch, etc...) but I'm also using mongoose so solution that uses Mongoose is OK.

NicolasMoise · Accepted Answer · 2014-05-12 16:37:02Z

3

You could use aggregation framework like this:

db.test312.aggregate(
    {$unwind:"$vehicles"},
    {$match:{"vehicles.name":"Nissan"}},
    {$group:{_id:"$_id",vehicles:{$push:"$vehicles"}}}
)

edited May 12, 2014 at 16:37

NicolasMoise

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answered May 12, 2014 at 16:33

Andrei Beziazychnyi

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4 Comments

NicolasMoise Over a year ago

How to I keep properties inside the main object? (e.g. { id: 123 , name: 'testName', vehicles : [ ... ] })

Andrei Beziazychnyi Over a year ago

Either by adding fields to {$group:{_id:{_id:"$_id",name:"$name"}}, vehic...} or by using {_id:"$_id",name:{$last:"$name"},vehic..}. In first case you need to add {$project:{}} after {$group} to unwrap _id

NicolasMoise Over a year ago

Thanks, I was kinda going the second way, but the first seems a bit cleaner

NicolasMoise Over a year ago

Actually I've encountered problem with that method: Follow-up: stackoverflow.com/questions/23636175/…

Rene Herget · Accepted Answer · 2014-05-15 10:29:30Z

1

You can use $addToSet on the group after unwinding and matching by listed equals true.

Sample shell query:

db.collection.aggregate([
{
    $unwind: "$vehicles"
},
{
    $match: {
        "vehicles.listed": {
            $eq: true
        }
    }
},
{
    $group: {
        _id: "$id",
        vehicles: {
            "$addToSet": {
                name: "$vehicles.name",
                listed: "$vehicles.listed"
            }
        }
    }
},
{
    $project: {
        _id: 0,
        id: "$_id",
        vehicles: 1
    }
}
]).pretty();

edited May 15, 2014 at 10:29

Rene Herget

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answered May 12, 2014 at 17:42

Lealem Admassu

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